A Subscriber Identity Module (SIM), such as a Removable User Identity Module (R-UIM), Universal Subscriber Identity Module (USIM), or GSM SIM, contains information relating to a user of a wireless communication device (WCD). A typical WCD may take the form of a cellular radiotelephone, satellite radiotelephone, a PCMCIA card incorporated within a computer, a PDA equipped with wireless communication capabilities, and the like.
A SIM typically includes a controller and memory housed in a card-like structure. The memory may contain user information including, for example, a subscriber/user identifier, a phonebook providing a stored bank of telephone numbers, messages, billing codes, encryption sequences for secure wireless data communication, and other useful information that can be retrieved during use. The memory also may store applications that are accessed by the WCD, e.g., for over-the-air service provisioning, cryptography, web browsing, or mobile commerce.
Typically, a SIM is removable, enabling a user to install the SIM in, or remove the SIM from, a WCD. The SIM can be removed from a first WCD, for example, and installed in a second WCD. In this manner, the SIM enables the user to transfer user information from one WCD to another WCD. This can be especially useful when the user travels to regions supported by different wireless protocols, which may require the use of a different WCD.
A SIM includes a relatively simple electrical interface, including an input/output (I/O) port for exchanging serial data with another device such as a WCD, a clock input for receiving an external clock signal, and a reset input for receiving a reset signal. A SIM ordinarily receives power from the device in which it is installed.
A WCD typically is powered by a rechargeable power source such as a Lithium Ion battery. Power consumption by the SIM can be a significant factor in overall WCD power consumption. A SIM consumes battery reserves and can reduce standby time for the WCD. Accordingly, efficient management of power consumption by a SIM is highly desirable.